The invention relates to a method for triggering a sensor-controlled lamp in which the incident light is detected via a light sensor, and via a control unit a luminous medium of the lamp is triggered as a function of the sensor signal, and to a sensor-controlled lamp having at least one sensor for detecting the incident light and having a control unit for triggering the lamp as a function of the sensor signal.
From German Patent Disclosure DE 195 14 973 A1, a fluorescent lamp is known in which the triggering of a ballast for the discharge vessel of the fluorescent lamp is carried out as a function of the signal of a light sensor, by which the incidence of light from the environment is detected.
One problem in such fluorescent lamps is that the incident light from the environment is superimposed on the incident lamp light itself, thus adulterating the signal detected by the light sensor. This problem is exacerbated by the fact that the spectrum of the light emitted by the discharge vessel changes after the lamp is started, since the proportion of infrared radiation immediately after the lamp is started is relatively high and drops off to a lower value again after a certain starting time (burn-in time). Hence when infrared sensors are used, the infrared light contained in normal daylight is augmented by the infrared component emitted in the burn-in phase, and thus the signal detected by the sensor is adulterated in the burn-in phase. This adulteration of the sensor signal can mean for instance that the fluorescent lamp initially starts as the ambient light fades, then turns off again after starting because the sensors, as a result of the infrared component of the lamp light itself, detect a signal that indicates greater brightness than is actually present, and so the lamp is turned off again despite the low incident light from the environment.
This disadvantage is overcome by DE 195 14 973 A1 by the provision that when the fluorescent lamp is started, an idle time member is switched, so that during a predetermined idle time, no triggering of the fluorescent lamp in response to a change in the sensor signals occurs. This idle time is adapted to the maximum burn-in duration of the discharge vessel, so that by the time the idle time has elapsed, the infrared component of the lamp light itself has dropped to a value that no longer adulterates the sensor signals in the way described above.
However, this known version is still problematic in that in the winter, for instance, at low outdoor temperatures, the burn-in duration of fluorescent lamps is substantially longer, because of the lower mercury vapor pressure, than in summertime at higher temperatures, and so under extreme conditions, the fixed idle time predetermined by the idle time member is shorter than the burn-in time that is established at low temperatures, and so even in this version, the above-described instabilities in the lamp triggering can still occur.
Similar problems arise when the fluorescent lamp is provided with an opaline covering, so that the infrared component emitted by the discharge vessel is reflected in the direction of the sensors to a greater extent than is the case in lamps with transparent coverings.
It is one object of the invention to provide a method for triggering a sensor-controlled lamp, and a sensor-controlled lamp itself, in which adulteration of the sensor signals by superimposed interference signals is minimized, even under unfavorable operating conditions.
To attain this and other objects, one aspect of the invention is directed to a method for triggering a sensor-controlled lamp in which the incident light is detected via a light sensor, and via a control unit (16) a luminous medium of the lamp is triggered as a function of the sensor signal. A change over time in the sensor signal is detected, and control parameters are defined for triggering the luminous medium as a function of the magnitude and of the change over time of the sensor signal.
Another aspect of the invention is directed to a sensor-controlled lamp, which is triggerable by the above-described method, having at least one sensor for detecting the incident light and having a control unit for triggering the lamp as a function of the sensor signal. A microprocessor detects a change over time in the sensor signal, stores the sensor signals, operating parameters and limit values in memory, and generates a control signal for changing an operating state of the lamp if the sensor signal exceeds or undershoots one of the limit values.
In accordance with preferred features of the invention, the lamp is provided with a microprocessor, by way of which the change in the sensor signal over time is detected on the basis of the incident light. As a function of these gradients in the sensor signal control parameters for triggering the luminous medium can then be defined. This makes it possible for the first time to control the triggering of the luminous medium as a function of the change over time in the incident light in such a way that external factors, such as temperature fluctuations, the type of coverings, sources of interference, etc., as well as the burn-in performance are detected via the gradient and taken into account in the triggering.
The control via the change over time in the control signal makes it possible, for instance, to detect the reduction in the infrared component of the lamp light itself during the burn-in phase extremely exactly, so that during the burn-in phase, the lamp can be operatedxe2x80x94regardless of the temperature, the condition of the lamp, the quality of the luminous medium, the power supply, the type of lamp covering, the mounted position, and so forthxe2x80x94in a mode in which the accidental light incidence causes no change in the operating state of the discharge vessel. Normal triggering of the lamp is effected only whenever the infrared component in the lamp light itself has faded, so that the change over time in the sensor signal is slight, because of the relatively constant incident light from the environment. In other words, this switchover is no longer dependent on a mean idle time that is adapted to typical operating conditions; instead, each time the fluorescent lamp is turned on, a new determination is made as a function of the operating conditions, so that proper functioning of the lamp is assured.
In conventional system, it was possible to effect a certain change in the turn-on and turn-off thresholds via external regulators that had to be adjusted manuallyxe2x80x94but these variants had to be readjusted as operating conditions (winter, summer, or place of use) changed, thus requiring considerable manual effort to make the necessary adaptations.
With an advantageous refinement of the invention, if a limit value of the change over time in the sensor signal is undershot, a turn-off or switching threshold is defined after each lamp starting event, which threshold is higher than the magnitude of the sensor signal by a predetermined value when the limit value is reached. In other words, in accordance with the invention these turn-off or switching thresholds are re-determined each time the lamp is started, making manual adaptation as in the above-described prior art is unnecessary. When this threshold value is reached, the lamp can for instance be turned off, since it can then be assumed that there is enough daylight. It is understood that instead of turning off the lamp, a switch can be made to other operating states instead, such as reducing the output, blinking, dimming, or the like.
Because of the detection of the change over time in the sensor signal, it is also possible to blank out interference signals from external extraneous lightxe2x80x94such as headlights of cars, floodlights of neighboring buildings, etc.xe2x80x94since as a rule these sources of accidental light are associated with an abrupt increase in brightness. That is, from the abrupt change in the control signal, the conclusion drawn is that an accidental light is present, and according to the invention an idle time is switched that runs until the accidental light no longer affects the ambient light. In other words, during this idle time the triggering of the discharge vessel is not changed.
To prevent an attendant excessively long burning of the discharge vessel, the turn-off threshold is raised as the idle time progresses, until it exceeds the sensor signal resulting from the accidental light. With the onset of brightness, the sensor signal then increases, so that despite the fact that accidental light is still present, the turn-off threshold is exceeded, and the discharge vessel is turned off.
Via the microprocessor, an emergency shutoff can also be predetermined, by way of which the lamp is turned off automatically if a predetermined maximum sensor signal is exceeded.
Detecting the incident light over time via the microprocessor makes it possible to detect a characteristic light curve as a function of a light changing cycle, such as a daily cycle, so that with a known characteristic light curve, a conclusion about the cycle time, such as the time of day, can be drawn from the change over time in the sensor signal. The function of the lamp can then be controlled as a function of this cycle time ascertained.
The fluorescent lamp of the invention is preferably embodied with two sensors, and the signals of the two sensors are evaluated in the microprocessor either independently of one another or jointly.
The lamp can be made especially compact if the microprocessor, the sensors and the lamp controller (ballast, etc.) are all received on a single common printed circuit board.
The operational reliability of the sensor-controlled lamp can be enhanced if a program for a test cycle is stored in the microprocessor and is run when the lamp is put into operation or if the sensors are arbitrarily covered. Within the scope of this test cycle, the lamp can be turned on and off at predetermined time intervals, for instance, so the user can easily be persuaded that the lamp is functional.